This invention relates to detergent compositions and more particularly to detergent compositions containing trisodium imidobis sulfate, tripotassium imidobis sulfate or mixtures thereof. The invention also relates to the use of such compositions in washing processes.
Detergent compositions containing a water soluble detergent surfactant and generally a builder which is used to sequester calcium and magnesium ions and to improve detergency levels of soaps and synthetic detergents, are widely used in home and industrial laundries for cleaning fabrics. Such detergent compositions may also contain fillers, such as sodium sulfate, and minor amounts of optical brighteners, soil antiredeposition agents, perfumes and the like. Although such detergent compositions effectively remove soil from fabrics, such as polyester, polyester/cotton, cotton and the like, certain stains, such as tea stains and grape juice stains, are very difficult to remove from fabrics using conventional detergent formulations.
To remove stains caused by tea, grape juice and the like, it is a common laundry practice to add a halogen-containing bleach, such as sodium hypochlorite, to remove such stains from fabrics. Although such halogen-containing bleaches can effectively remove the stain, such stain removal is accompanied by some damage to dyed fabrics. It is also desirable, if not necessary, to segregate white clothes from colored clothes to minimize the deleterious effect of normal use levels of chlorine-containing bleaches on colored fabrics and to prevent transfer of dye from colored fabrics to white fabrics.
To overcome these problems, those skilled in the art of detergent formulations have long been interested in a material that would mitigate the deleterious effect of halogen-containing bleaches on fabrics, particularly colored fabrics, without loss of desirable bleaching properties. Compounds heretofore considered which mitigated the deleterious effect of halogen-containing bleaches on colored fabrics also prevented adequate bleaching of stains.
Now, a material has been found that permits adequate bleaching of stains during washing while mitigating the damaging effects of halogen-containing bleaches on colored fabrics, permitting the formulation of new and novel detergent compositions. Such an improved laundry detergent formulation permits the use of halogen-containing bleaches with colored fabrics with reduced fear of damage to the color. Moreover, the necessity for separating colored fabrics from white fabrics during the wash/bleach operation is reduced or even eliminated.
This bleach damage mitigating effect is achieved by adding an alkali metal salt of imidobis sulfuric acid, such as trisodium imidobis sulfate, tripotassium imidobis sulfate or mixtures thereof to the detergent composition. Such compounds and methods of their preparation are known to the art (see for example, J. W. Mellor, "A comprehensive Treatice on Inorganic and Theoretical Chemistry," Longmans, Green & Co., Ltd., London, 1931, Vol. VIII, pages 647 through 660). It is most economically made from ammonia, sulfur trioxide and sodium hydroxide as basic raw materials. More recently, several Japanese patents relating to process reactor design, crystalline trisodium salts and hydrates and the use of trisodium imidobis sulfate as a builder to replace sodium tripolyphosphate (STP) in detergent formulations have appeared (see for example, Japanese Pat. Nos. 71,06,495; 73,132,772; 74,119,983; and 75,132,772). However, our evaluation indicated that trisodium imidobis sulfate was a rather poor detergent builder, having about 25 percent of the effectiveness of STP; and while it might be effective as a builder in detergent formulations for use in relatively soft water having less than about 50 ppm (as CaCO.sub.3) of hardness, in water having more than about 50 ppm of hardness, a builder having a stronger binding affinity for calcium and magnesium ions, such as STP, would be necessary in order to provide the desired optimum detergent builder characteristics.
Now it has been found that a detergent formulation can be prepared in which trisodium imidobis sulfate acts not as a builder but as a special additive which will mitigate the effect of halogen-containing bleaches on colored fabrics while still permitting the bleach to have its desired end effect on undesirable stains and on vagrant dyes in solution. The use of such a detergent formulation along with bleach reduces the necessity for the housewife or industrial laundry to segregate white fabrics from colored fabrics during the washing cycle and is of particular interest when, for example, printed fabrics containing a mixture of white and colors are cleaned. Colored fabrics washed in the detergent composition of the present invention maintain their color brightness almost as though no bleach were present.